This invention relates to a breakerless and distributorless multiple cylinder ignition system and particularly to an alternator driven ignition system adapted for multiple cylinder two cycle motors and the like.
The advances in the technology of solid state devices and alternator constructions has resulted in the development of alternator driven capacitor discharge ignition systems.
In capacitor discharge systems, a main firing capacitor is charged to a relatively high voltage level and then rapidly discharged, by actuation of a solid state switch such as a controlled rectifier, through suitable pulse transformer to generate and transmit the firing energy to a selected spark plug. The capacitor may be charged from a battery power supply through a DC to DC converter. Alternatively, and, in particular, for relatively small engines such as in low horsepower outboard motors, an alternator is advantageously employed to produce an alternating current output which is rectified and applied to charge the capacitor. A trigger generator signal means preferably forms a part of the alternator unit to produce a signal for proper timed activation of the solid state switch to discharge the capacitor. A distributor may be employed to distribute the energy to anyone of a plurality of cylinders in a multiple cylinder engine, or alternatively separate coupling circuits may be provided with steering means to selectively transfer the energy to the several discharge circuits. Thus, the conventional rotating distributor is, in essence, replaced with an electronic steering and power distributing circuit. For example, the U.S. Pat. No. 3,612,948 discloses an alternator driven capacitor discharge ignition system wherein a common capacitor is selectively coupled through individual solid state switches to individual pulse forming and firing circuits to the several spark plugs of a dual or two cylinder engine. A charging alternator is provided to charge the capacitor and a separate triggering alternator is provided to fire the switches in predetermined timed relation for accurate and proper discharge of the capacitor through the several circuits. An alternative system employing an alternator having a single magnetic rotor and, a plurality of windings wound on a common stator is shown in U.S. Pat. No. 3,358,665.
In ignition systems, means are advantageously provided to vary the ignition timing of the engine by varying the relative time of generating the firing pulse. Thus, the engine is normally started with a retard firing, that is, with the firing occurring slightly after a piston reaches top dead center position. As the speed increases, the time of firing is preferably advanced from said top dead center position. Various electronic circuits as well as mechanical leverage systems have been suggested to produce a controlled advance. For example, U.S. Pat. No. 2,906,251 discloses a cam arrangement interconnected through a throttle unit for providing an interrelationship between the firing of a breakerpoint system and the throttle setting.
When applied to relatively small engines such as a two cylinder engine for an outboard motor, the overall size of the mechanical construction also becomes somewhat more significant. From an aesthetic standpoint, the overall height of the engine and thereby the power head for low HP motors is preferably minimized. As the alternators are normally incorporated into the flywheel structure, the design preferably minimizes the vertical space requirements so as to permit lowering of the flywheel to a maximum thereby maintaining the desired lower profile. The construction, of course, must not however sacrifice the alternator output such that it falls below the level required for reliable and satisfactory ignition as well as providing means to maintain proper timing.
Further in all such ignition systems, the cost of both the initial construction and subsequent maintenance from a mechanical and electrical standpoint must be and is of substantial practical significance and consideration.